1. Field of the Invention
The present invention relates to a non-contact rotation angle detecting sensor using a magnetic responsive element.
2. The Related Art of the Invention
As a rotation angle sensor, for example, suitable for detecting a depressing angle of an accelerator pedal or detecting a rotation angle of a shaft rotating in accordance with an operation of shift lever for a vehicle, which is portable and has no possibility of contact defect due to a foreign matter, there is a non-contact rotation angle sensor using a magnetic responsive element.
Japanese Unexamined Publication No. 5-505883 has disclosed, for example, a conventional example of such a non-contact rotation angle sensor.
In this conventional example, as shown in FIG. 7A, a ring-shape permanent magnet 100 which is divided in a semi circle is fixed to a rotor (not shown) to form two poles, N and S in a diameter direction, and on the other hand, an outer periphery of the permanent magnet is surrounded by an outside yoke 110 in a predetermined distance therefrom and a hole element 105 is disposed in a gap provided in the outside yoke 110. The outside yoke 110 has a rectangular cross section, the width and the axial height of which are respectively constant in the circumferential direction.
In the above arrangement, magnetic flux generated from the ring-shaped permanent magnet 100 passes through the outside yoke 110. When the ring-shaped permanent magnet rotates with the rotor, since the axial height of the outside yoke 110 facing the magnet is constant, a sum of the magnetic flux passing through the outside yoke 110 is constant, but a ratio of an amount of the magnetic flux passing through the hole element 105 disposed in the gap of the outside yoke 110 to an amount of the magnetic flux not passing through the hole element 105 changes with rotation of ring-shaped permanent magnet 100.
Thereby, a rotation angle of the rotor (ring-shaped permanent magnet 100) can be theoretically determined from change in output of the hole element 105.
A to E in FIG. 7A, show an amount of the magnetic flux passing through the hole element 105 with rotation of the ring-shaped permanent magnet 100. FIG. 7B shows an output of the hole element 105 to a rotation angle and A to E on the line correspond to each rotation angle position of the ring-shaped permanent magnet 100 in FIG. 7A.
In the conventional non-contact rotation angle detecting sensor, however, as shown in FIG. 7B, an output change of the hole element 105 is clear in a predetermined range B to D including a rotation angle 0° where the direction of the magnetic flux passing through the hole element 105 changes, but there occurs the problem with linearity of an output signal as deviated out of the predetermined range.
It is assumed that this is because an amount of the magnetic flux passing through the hole element 105 increases as deviated out of the predetermined range, while a change rate of the magnetic flux becomes relatively small.
When the linearity of the output signal of the hole element is not maintained in this way, there is the problem that a desired accuracy can not be provided in a case a rotation angle is required to be detected over a relatively wide angle range.
Coping with this, it is considered that the ring shape of the outside yoke is formed in an elliptic shape or a clearance between the outside yoke and the permanent magnet is changed. However, these are theoretical measures, and in fact, it is technically difficult to apply these measures to a case of mass production such as a vehicle in consideration of variations in the manufacture or technical variations in products.
In addition, as a ring-shaped permanent magnet, there are many examples using an anisotropic magnet. However, there is the problem that the anisotropic magnet is expensive and is in lack of workability.
In view of the above, there exists a need for anon-contact rotation angle detecting sensor which overcomes the above-mentioned problems in the related art. The present invention addresses this need in the related art and also other needs, which will become apparent to those skilled in the art from this disclosure.